accel/mshv: Add accelerator skeleton

Introduce the initial scaffold for the MSHV (Microsoft Hypervisor)
accelerator backend. This includes the basic directory structure and
stub implementations needed to integrate with QEMU's accelerator
framework.

Signed-off-by: Magnus Kulke <magnuskulke@linux.microsoft.com>
Link: https://lore.kernel.org/r/20250916164847.77883-8-magnuskulke@linux.microsoft.com
[Move include of linux/mshv.h in the per-target section; create
 include/system/mshv_int.h. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

accel/meson.build

@@ -10,6 +10,7 @@ if have_system
   subdir('kvm')
   subdir('xen')
   subdir('stubs')
+  subdir('mshv')
 endif
 
 # qtest

accel/mshv/meson.build

@@ -0,0 +1,6 @@
+mshv_ss = ss.source_set()
+mshv_ss.add(if_true: files(
+  'mshv-all.c'
+))
+
+specific_ss.add_all(when: 'CONFIG_MSHV', if_true: mshv_ss)

accel/mshv/mshv-all.c

@@ -0,0 +1,144 @@
+/*
+ * QEMU MSHV support
+ *
+ * Copyright Microsoft, Corp. 2025
+ *
+ * Authors:
+ *  Ziqiao Zhou       <ziqiaozhou@microsoft.com>
+ *  Magnus Kulke      <magnuskulke@microsoft.com>
+ *  Jinank Jain       <jinankjain@microsoft.com>
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ *
+ */
+
+#include "qemu/osdep.h"
+#include "qapi/error.h"
+#include "qemu/error-report.h"
+#include "qemu/event_notifier.h"
+#include "qemu/module.h"
+#include "qemu/main-loop.h"
+#include "hw/boards.h"
+
+#include "hw/hyperv/hvhdk.h"
+#include "hw/hyperv/hvhdk_mini.h"
+#include "hw/hyperv/hvgdk.h"
+#include "linux/mshv.h"
+
+#include "qemu/accel.h"
+#include "qemu/guest-random.h"
+#include "accel/accel-ops.h"
+#include "accel/accel-cpu-ops.h"
+#include "system/cpus.h"
+#include "system/runstate.h"
+#include "system/accel-blocker.h"
+#include "system/address-spaces.h"
+#include "system/mshv.h"
+#include "system/mshv_int.h"
+#include "system/reset.h"
+#include "trace.h"
+#include <err.h>
+#include <stdint.h>
+#include <sys/ioctl.h>
+
+#define TYPE_MSHV_ACCEL ACCEL_CLASS_NAME("mshv")
+
+DECLARE_INSTANCE_CHECKER(MshvState, MSHV_STATE, TYPE_MSHV_ACCEL)
+
+bool mshv_allowed;
+
+MshvState *mshv_state;
+
+static int mshv_init(AccelState *as, MachineState *ms)
+{
+    error_report("unimplemented");
+    abort();
+}
+
+static void mshv_start_vcpu_thread(CPUState *cpu)
+{
+    error_report("unimplemented");
+    abort();
+}
+
+static void mshv_cpu_synchronize_post_init(CPUState *cpu)
+{
+    error_report("unimplemented");
+    abort();
+}
+
+static void mshv_cpu_synchronize_post_reset(CPUState *cpu)
+{
+    error_report("unimplemented");
+    abort();
+}
+
+static void mshv_cpu_synchronize_pre_loadvm(CPUState *cpu)
+{
+    error_report("unimplemented");
+    abort();
+}
+
+static void mshv_cpu_synchronize(CPUState *cpu)
+{
+    error_report("unimplemented");
+    abort();
+}
+
+static bool mshv_cpus_are_resettable(void)
+{
+    error_report("unimplemented");
+    abort();
+}
+
+static void mshv_accel_class_init(ObjectClass *oc, const void *data)
+{
+    AccelClass *ac = ACCEL_CLASS(oc);
+
+    ac->name = "MSHV";
+    ac->init_machine = mshv_init;
+    ac->allowed = &mshv_allowed;
+}
+
+static void mshv_accel_instance_init(Object *obj)
+{
+    MshvState *s = MSHV_STATE(obj);
+
+    s->vm = 0;
+}
+
+static const TypeInfo mshv_accel_type = {
+    .name = TYPE_MSHV_ACCEL,
+    .parent = TYPE_ACCEL,
+    .instance_init = mshv_accel_instance_init,
+    .class_init = mshv_accel_class_init,
+    .instance_size = sizeof(MshvState),
+};
+
+static void mshv_accel_ops_class_init(ObjectClass *oc, const void *data)
+{
+    AccelOpsClass *ops = ACCEL_OPS_CLASS(oc);
+
+    ops->create_vcpu_thread = mshv_start_vcpu_thread;
+    ops->synchronize_post_init = mshv_cpu_synchronize_post_init;
+    ops->synchronize_post_reset = mshv_cpu_synchronize_post_reset;
+    ops->synchronize_state = mshv_cpu_synchronize;
+    ops->synchronize_pre_loadvm = mshv_cpu_synchronize_pre_loadvm;
+    ops->cpus_are_resettable = mshv_cpus_are_resettable;
+    ops->handle_interrupt = generic_handle_interrupt;
+}
+
+static const TypeInfo mshv_accel_ops_type = {
+    .name = ACCEL_OPS_NAME("mshv"),
+    .parent = TYPE_ACCEL_OPS,
+    .class_init = mshv_accel_ops_class_init,
+    .abstract = true,
+};
+
+static void mshv_type_init(void)
+{
+    type_register_static(&mshv_accel_type);
+    type_register_static(&mshv_accel_ops_type);
+}
+
+type_init(mshv_type_init);

include/system/mshv.h

@@ -14,8 +14,17 @@
 #ifndef QEMU_MSHV_H
 #define QEMU_MSHV_H
 
+#include "qemu/osdep.h"
+#include "qemu/accel.h"
+#include "hw/hyperv/hyperv-proto.h"
+#include "hw/hyperv/hvhdk.h"
+#include "qapi/qapi-types-common.h"
+#include "system/memory.h"
+#include "accel/accel-ops.h"
+
 #ifdef COMPILING_PER_TARGET
 #ifdef CONFIG_MSHV
+#include <linux/mshv.h>
 #define CONFIG_MSHV_IS_POSSIBLE
 #endif
 #else
@@ -30,6 +39,9 @@ extern bool mshv_allowed;
 #endif
 #define mshv_msi_via_irqfd_enabled() false
 
+typedef struct MshvState MshvState;
+extern MshvState *mshv_state;
+
 /* interrupt */
 int mshv_irqchip_add_msi_route(int vector, PCIDevice *dev);
 int mshv_irqchip_update_msi_route(int virq, MSIMessage msg, PCIDevice *dev);

include/system/mshv_int.h

@@ -0,0 +1,41 @@
+/*
+ * QEMU MSHV support
+ *
+ * Copyright Microsoft, Corp. 2025
+ *
+ * Authors: Ziqiao Zhou  <ziqiaozhou@microsoft.com>
+ *          Magnus Kulke <magnuskulke@microsoft.com>
+ *          Jinank Jain  <jinankjain@microsoft.com>
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ *
+ */
+
+#ifndef QEMU_MSHV_INT_H
+#define QEMU_MSHV_INT_H
+
+struct AccelCPUState {
+    int cpufd;
+    bool dirty;
+};
+
+typedef struct MshvMemoryListener {
+    MemoryListener listener;
+    int as_id;
+} MshvMemoryListener;
+
+typedef struct MshvAddressSpace {
+    MshvMemoryListener *ml;
+    AddressSpace *as;
+} MshvAddressSpace;
+
+struct MshvState {
+    AccelState parent_obj;
+    int vm;
+    MshvMemoryListener memory_listener;
+    /* number of listeners */
+    int nr_as;
+    MshvAddressSpace *as;
+};
+
+#endif